1. Field of the Invention
The present invention relates to a lithographic projection apparatus.
2. Description of the Related Art
The term xe2x80x9cpatterning devicexe2x80x9d as here employed should be broadly interpreted as referring to device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term xe2x80x9clight valvexe2x80x9d can also be used in this context. Generally, the pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). An example of such a patterning device is a mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired.
Another example of a pattering device is a programmable mirror array. One example of such an array is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that, for example, addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind. In this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. An alternative embodiment of a programmable mirror array employs a matrix arrangement of tiny mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing piezoelectric actuators. Once again, the mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors. In this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronics. In both of the situations described hereabove, the patterning device can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be seen, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096, which are incorporated herein by reference. In the case of a programmable mirror array, the support structure may be embodied as a frame or table, for example, which may be fixed or movable as required.
Another example of a pattering device is a programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the support structure in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table. However, the general principles discussed in such instances should be seen in the broader context of the patterning device as hereabove set forth.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning device may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once. Such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction. Since, in general, the projection system will have a magnification factor M (generally  less than 1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be seen, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
In a known manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4.
For the sake of simplicity, the projection system may hereinafter be referred to as the xe2x80x9clens.xe2x80x9d However, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the beam of radiation, and such components may also be referred to below, collectively or singularly, as a xe2x80x9clensxe2x80x9d. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such xe2x80x9cmultiple stagexe2x80x9d devices the additional tables may be used in parallel or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Dual stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, incorporated herein by reference.
A projection apparatus, such as used in lithography, generally includes an illumination system, referred to hereafter simply as an illuminator. The illuminator receives radiation from a source, such as a laser, and produces a projection beam for illuminating an object, such as the patterning device (e.g. a mask on a mask table). Within a typical illuminator, the beam is shaped and controlled such that at a pupil plane the beam has a desired spatial intensity distribution. This spatial intensity distribution at the pupil plane effectively acts as a virtual radiation source for producing the projection beam. A Following a first pupil plane, the radiation is substantially focused by a lens group referred to hereafter as xe2x80x9ccoupling Lensxe2x80x9d. The coupling lens couples the substantially focused radiation into an integrator, such as a quartz rod. The function of the integrator is to improve the homogeneity of the spatial and/or angular intensity distribution of the projection beam. The spatial intensity distribution at the pupil plane is converted to an angular intensity distribution at the object being illuminated by the coupling optics, because the pupil plane substantially coincides with the front focal plane of the coupling optics. Controlling the spatial intensity distribution at the pupil plane can be done to improve the processing latitudes when an image of the illuminated object is projected onto a substrate. In particular, spatial intensity distributions with dipole, annular or quadrupole off-axis illumination profiles have been proposed to enhance the resolution and other parameters of the projection, such as sensitivity to projection lens aberrations, exposure latitude and depth of focus.
A known illuminator comprises an optical system referred to hereafter as xe2x80x9czoom-axiconxe2x80x9d. The zoom-axicon is a device that adjusts the intensity distribution at the pupil plane. Radiation from the source passes through a first optical element such as, for example, a diffractive optical element (DOE), which generates an angular intensity distribution. Next, the radiation beam traverses a zoom lens. In the back focal plane of the zoom lens a spatial intensity distribution occurs that generally is suitable to serve as a secondary light source in the pupil plane. Hence the back focal plane of the zoom lens typically substantially coincides with the pupil plane (i.e. the front focal plane of the coupling optics). The outer radial extent of the spatial intensity distribution at the pupil plane can be changed by changing the focal length of the zoom lens. However, the zoom lens must have two degrees of freedom, one to change the focal length of the zoom lens and a second to change the position of the principal planes such that when the focal length changes, the back focal plane remains located at the pupil plane of the illuminator. Due to this functionality, the zoom lens typically consists of several (e.g. at least three) separate lenses in series, several of which are movable. As mentioned above, by tuning the focal length of the zoom lens, the radial extent of the intensity distribution at the pupil plane can be set. In the following, any preselected, preferred spatial intensity distribution at the pupil plane may be referred to as an xe2x80x9cillumination settingxe2x80x9d.
An axicon, which is located near the pupil plane, generally consists of two elements having complimentary conical shaped faces. The axicon is used to generate annular spatial intensity distributions, or other spatial intensity distributions with substantially no intensity around their center, i.e. no on-axis illumination. By tuning the distance between the two conical faces of the axicon, the annularity can be adjusted. When the axicon is closed, i.e. the gap between the conical faces is zero, conventional, (i.e. disc-like) illumination settings can be produced. With a gap between the conical faces, an annular intensity distribution results, with the inner radial extent of the annulus determined by the distance between the two conical faces. On the other hand the zoom lens determines the outer radial extent and thus the width of the annulus. Preselected inner and outer radial extents of the intensity distribution are often referred to as "sgr"-settings, in particular the "sgr"-inner settings and the "sgr"-outer setting, respectively. Here, "sgr"-inner and "sgr"-outer are a measure for the ratio of the radius in question to the maximum radius of the pupil.
The term xe2x80x9czoom-axiconxe2x80x9d as employed here should be interpreted as referring to a module comprising a zoom lens and an axicon.
Multiple illumination settings can be generated by various device in the known illuminator, for example by modifying the first optical element in front of the zoom lens, such as to appropriately shape the angular intensity distribution, or by inserting aperture plates or blades into the beam path, for instance near a pupil plane, and so on. Further information on a known zoom-axicon module and multipole mode generation are given (for example) in U.S. Pat. No. 6,452,662, incorporated herein by reference.
In the known illuminator, described above, it is apparent that to produce the desired range of illumination settings the zoom-axicon module will generally have several (e.g. five or more) optical components, which can make it expensive to produce, particularly given the fact that several of the elements must be independently movable. A further problem is that the lenses comprising the zoom lens and the two conical elements of the axicon represent a considerable thickness of lens material and a large number of surface interfaces. This means that the transmission efficiency can be poor due to absorption, reflection, inefficient coatings, degradation effects and contamination. This problem is exacerbated by the demand for imaging ever smaller features at higher densities, which requires the use of radiation with shorter wavelengths, such as 193, 157, 126 nm or even EUV (e.g. 5-20 nm). The efficiency of suitable transmissive materials, such as CaF2 and quartz, decreases at shorter wavelengths due to increased absorption and no materials are known that are sufficiently transmissive for EUV radiation. The effectiveness of the optical coatings of the components also typically decreases at shorter wavelengths and degradation effects generally become worse. Thus, overall, a significant throughput reduction can occur, due to decreased transmission. Another problem is that the known illuminator occupies a relatively large volume in the lithography apparatus. This in turn can lead to excess bulk in the machine, and increased manufacturing costs (particularly when using material such as CaF2).
As mentioned above, spatial intensity distributions with dipole, annular or quadrupole off-axis illumination profiles can enhance the projection properties. The choice of the profile depends on, amongst others, the respective application of the lithographic process. To provide a desired non-standard illumination mode for a given application, requires dedicated optical devices which must be specially designed at considerate effort and expense.
EP 0 744 641 A describes an illumination system for use in a lithography apparatus which uses a deformable mirror to improve the uniformity of illumination of the mask.
EP 0 486 316 A describes various different lithography apparatus including a variety of different arrangements for providing dipole and quadrupole illumination settings. These include arrangements using fiber bundles whose exit points are moveable to define the pole positions. Other arrangements use a mirror shiftable between two positions during an exposure or between shots of a multishot exposure.
An aspect of the present invention is to provide an improved lithography apparatus with an illuminator which avoids or alleviates the above problems. A further object is to provide devices which can be used to generate nearly any desired intensity distribution of the projection beam.
According to one aspect of the present invention there is provided a lithographic apparatus including a radiation system to provide a projection beam of radiation; a support structure for supporting a patterning device, the patterning device serving to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; a projection system to project the patterned beam onto a target portion of the substrate; wherein the radiation system comprises an illumination system configured to define the intensity distribution of the projection beam, wherein the illumination system comprises a steering device to individually steer different parts of an incoming beam into different directions to provide a desired angular intensity distribution of the projection beam at the patterning device, the steering device comprising a plurality of discrete mirrors, each for steering a part of the incoming beam and whose orientation can be controlled individually to direct the corresponding part of the incoming beam into a desired direction.
Another aspect of the present invention the plurality of discrete mirrors. Preferably, the discrete mirrors can be controlled to direct their corresponding part of the incoming beam into (substantially) any desired direction. The resulting angular intensity distribution can then be transformed into a spatial intensity distribution, for example by a focusing lens. Examples for a directing element are a reflecting element, which reflects the incident radiation into a direction or range of directions, and a diffractive element, which diffracts and thereby diverges the incident radiation. Any other type of element which is capable of directing radiation into a specific direction or range of directions or into plural directions can be used as a directing element, as long as the direction or the directions can be controlled. The control can be performed by any suitable way, for example mechanically to orient the directing element and/or electrically to directly or indirectly change the directing properties and/or the orientation of the directing element. Other methods for influencing the directing element and thereby setting the direction or directions are possible, such as methods using electromagnetic radiation or fields.
In recent times, micro-electromechanical and micro-opto-electro-mechanical systems (MEMS and MOEMS) have been developed for use as optical switches in devices for optical data transmission. Some of these MEMS comprise arrays with more than 1000 microscopic mirrors wherein each of the mirrors can be tilted in two different planes perpendicular to each other. Thus, radiation incident on such devices can be reflected into (substantially) any desired direction of a hemisphere. Such an array of reflective elements can be used as the plurality of discrete mirrors and are individually oriented to reflect projection radiation into different pre-determined directions.
An important advantage of the present invention lies in the fact that it can be applied to EUV radiation to provide desired intensity distributions. It has up to now not been possible to provide a zoom-axicon or equivalent device that would function with EUV radiation.
In a particular embodiment of the invention, the steering device includes a first faceted mirror, each of the discrete mirrors being a facet of the first faceted mirror and serving to project an image of a radiation source onto a selected facet of a second faceted mirror by control of the orientation thereof. In this arrangement, the first faceted mirror acts as a field mirror and a fly""s-eye reflector, creating a large number of virtual sources on the second faceted mirror which are then redirected to overlap on the mask, providing the desired uniformity of illumination. Preferably, the second faceted mirror is in a plane conjugate with a pupil plane of the projection system so that the illumination of the second faceted mirror determines the illumination mode of the mask. Thus, the illumination mode can be controlled by controlling the orientation of the facets of the first faceted mirror to illuminate selected ones of the facets of the second faceted mirror. This avoids the loss of beam intensity that would occur if the illumination mode is set by selective masking in a pupil plane.
The present invention is not limited to the case that the radiation system provides a single projection beam of radiation. Rather, different sub-beams or bundles of sub-beams can be generated at different locations and can be steered by the steering device to produce the desired angular intensity distribution. Furthermore, the projection beam or at least one of the projection beams can be split up to form separate sub-beams before reaching the directing elements. This means that the angular intensity distribution may be somewhat influenced by the manner in which the projection beam or projection beams is generated or manipulated before reaching the directing elements, but the control of the directing elements enables the user to produce the desired angular intensity distribution by choosing from a wide range of possible distributions. In particular, it is preferred that the directing elements can be controlled to direct each incident part of the projection radiation into (substantially) any direction of a hemisphere.
As described above, a desired spatial intensity distribution is to be produced in some cases. In these cases, it is preferred to produce a corresponding angular intensity distribution and to use a re-directing element to at least a part of the steered projection beam to produce the desired spatial intensity distribution in a cross-section of the projection beam, in particular in a focal plane. In particular, if focusing optical elements are used, such as a convex lens, each of the different directions of radiation propagation (of the produced angular intensity distribution) corresponds to one particular area of the spatial intensity distribution, in particular to one specific local point in a focal plane.
Different shapes and/or profiles of such a spatial intensity distribution such as annular, quadrupole, dipole and (soft) multipole, have been proposed. The present invention enables the user of a lithographic projection apparatus to produce any desired spatial intensity distribution, for example with arbitrary, definable shapes.
According to a preferred aspect of the invention, at least some of the sub-beams are steered and re-directed so that they correspond to spots or dashes of radiation in the cross-section in which the spatial intensity distribution is defined. Thus, the spatial intensity distribution has a profile with a discrete character. Depending on the size of the spots and/or dashes, and thereby depending on the size of the range of directions into which a single sub-beam is steered by the steering device, the spatial intensity distribution can comprise zones where the intensity is zero or almost zero (non-illuminated or dark zones) between illuminated areas.
In a preferred embodiment, the range of directions into which a single sub-beam propagates is influenced so that there is a sufficiently continuous intensity distribution. It is possible to influence the respective sub-beam or beams before the beam reaches the directing element and/or afterwards. In one particular embodiment, the sub-beams are steered so that they each propagate essentially to a single point. The points can be the same or different for the different sub-beams. One advantage of this embodiment is that the sub-beam can easily be adjusted to be incident on the directing element in the correct place. Further, undesired boundary effects due to radiation which is incident at the boundaries of the directing element can be reduced or avoided. For example, if the directing element is a reflective element with a given size of a reflective area, the arrangement can easily be adjusted so that the sub-beam is incident on the reflective element in the central zone of the reflective area.
To increase the range of propagation directions of the steered sub-beam, a diffuser device, such as a diffuser plate, can be used. However, this also may affect the polarization of the sub-beam and can make it difficult or impossible to exploit the polarization in subsequent stages.
In another embodiment, the sub-beam or beams are therefore manipulated before reaching the directing element or elements. In particular, the respective sub-beam is manipulated so that the steered sub-beam propagates into a defined range of propagation directions. For example, this can be done using a concentrating element to concentrate the sub-beam onto the directing element. The concentration also has the advantage that the sub-beam is incident on the directing element at the correct place, e.g. the central zone of a reflective area.
In addition or alternative to the embodiments described before, the range of propagation directions of the sub-beam or beams can be increased using the directing element or elements. In particular, the reflective surface area of a reflective element can be shaped accordingly, for example to have a convex shape.
The term xe2x80x9csub-beamxe2x80x9d as here employed should not be interpreted in a limiting way regarding the intensity distribution of the beam or beams before reaching the directing elements. Rather, the respective beam can be a single beam with a continuous intensity distribution, but, at the same time, can be considered to comprise a bundle of sub-beams. At least some of the sub-beams may become individual beams, separated from other parts of the beam, after being steered by the steering device. In any case, each steered sub-beam corresponds to a related part of the originally generated projection beam or beams.
Another aspect of the invention is that a variety of intensity distributions of the projection beam can be produced without the need to design corresponding optical arrangements especially for each one particular illumination setting and/or to replace at least parts of an existing optical arrangement. In particular, intensity distributions can be produced which previously existed only in theory.
According to a further aspect of the invention there is provided a device manufacturing method including providing a substrate at least partially with a layer of radiation-sensitive material; providing at least one projection beam of radiation; modifying the intensity distribution of the projection beam; using a patterning device to endow the modified projection beam with a pattern in its cross-section; projecting the patterned beam of radiation onto a target which comprises at least a part of the radiation-sensitive material, wherein the modification of the intensity distribution of the projection beam includes controlling the direction into which the radiation propagates, wherein the projection beam comprises a plurality of sub-beams, wherein at least some of the sub-beams are steered into different directions using a plurality of directing elements, and wherein the directing elements are individually controlled to direct the corresponding sub-beam into a desired direction.
According to still a further aspect of the invention there is provided a control system for controlling the intensity distribution of a beam of radiation for use in lithography including a calculation unit for calculating, based on a given intensity distribution of the beam, the necessary modifications to be made to the given distribution to produce a desired intensity distribution; an input device to input information about the desired intensity distribution; an output device to output a plurality of control signals to a plurality of directing elements which are capable of re-directing parts of the beam; wherein the calculation unit is adapted to calculate the control signals so that the directing elements can be controlled to modify the given intensity distribution of the beam to an angular intensity distribution which corresponds to the desired intensity distribution.
The calculation unit calculates the control signals based on a given intensity distribution. In particular, the given intensity distribution is applied in a projection beam of radiation which is used repeatedly to project the same pattern onto respective radiation-sensitive areas of one or more than one substrate. In one scenario, the given intensity distribution will be the same for each projection period, which may be interrupted by time periods with no illumination of radiation-sensitive material. However, it is also possible to employ different intensity distributions one after the other, using the same plurality of directing elements. In this case, the control system outputs different sets of control signals to the plurality of directing elements in order to change the angular intensity distribution between two projection periods.
In particular if the directing elements are electrically controlled, the illumination setting can be changed very quickly, due to the small mass and inertia of single, individually controllable directing elements compared to the mass and inertia of whole sets of optical elements, such as sets of diffractive optical elements with many microlenses. Thus, it is now possible to change the illumination setting between two flashes of illumination in acceptable time and to employ different intensity distributions alternatingly on a substrate.
According to a further aspect of the present invention there is provided a control system for controlling the intensity distribution of a beam of radiation for use in lithography including a calculation unit for calculating, based on a given intensity distribution of the beam, the necessary modifications to be made to the given distribution to produce a desired intensity distribution; an input device to input information about the desired intensity distribution; an output device to output a plurality of control signals to a plurality of discrete reflectors which are capable of re-directing parts of the beam, wherein the calculation unit is adapted to calculate the control signals so that the orientation of the discrete reflectors can be controlled to modify the given intensity distribution of the radiation beam to an angular intensity distribution which corresponds to the desired intensity distribution.
The control system may also be provided with an input device to receive the actually obtained mirror positions and/or pupil distribution so as to effect a closed loop control of the minor position and/or pupil distribution. The pupil distribution may be measured as described in European Patent Application No. 00307558.7, which is hereby incorporated by reference.
According to still a further aspect of the invention there is provided a computer program for producing a desired spatial intensity distribution of a beam of radiation for use in lithography, wherein an angular intensity distribution of radiation propagation of the beam corresponds to a spatial intensity distribution in a cross-section of the beam; and a steering device can be controlled to form an angular intensity distribution for any desired spatial intensity distribution by re-directing parts of the beam; the computer program comprising a code adapted to calculate the necessary state of the steering device and/or the control signals for controlling the steering device to form the angular intensity distribution which corresponds to the desired spatial intensity distributions.
In a preferred embodiment, an arbitrary spatial intensity distribution in a cross-section of the beam can be defined and the code is adapted to calculate the necessary state of the steering device and/or the control signals to form the corresponding angular intensity distribution.
In general, it is not possible to produce any theoretically possible angular intensity distribution. In particular, if the steering device includes directing elements as described above, there will be some discrete character of the intensity distribution due to the fact that each directing element directs the corresponding part of the beam into a limited range of directions only (see above). Depending on the number of directing elements, on their characteristic properties, and other factors, the discrete character of the intensity distribution will be more or less pronounced. It is preferred that the code of the computer program take the discrete character into account and calculate the necessary state of the steering device and/or the control signals which result in the closest approximation of the angular intensity distribution which is equivalent to the desired spatial intensity distribution.
Preferably, in order to increase the number of spatial intensity distributions which can be produced by transforming the angular intensity distribution to the corresponding spatial intensity distribution, the optical elements (e.g. zoom lens) which transforms the angular intensity distribution to the spatial distribution can be modified and/or exchanged. In this case, the computer program must have access to the amended transformation behavior. In a preferred embodiment, the code is adapted to choose between different transformation arrangements and/or properties of transformation arrangements and are adapted to calculate not only the state of the steering device and/or the control signals for controlling the steering device, but are also adapted to calculate the corresponding transformation arrangement which produces the desired spatial intensity distribution. For example, the transformer may include a zoom lens and the code are then adapted to choose or calculate an appropriate value of the focal length of the zoom lens.
Alternatively, or as an added feature, it is possible that the code can choose between different arrangements for influencing the projection beam before it reaches the steering device.
Although specific reference may be made in this text to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. One of ordinary skill will appreciate that, in the context of such alternative applications, any use of the terms xe2x80x9creticlexe2x80x9d, xe2x80x9cwaferxe2x80x9d or xe2x80x9cdiexe2x80x9d in this text should be considered as being replaced by the more general terms xe2x80x9cmaskxe2x80x9d, xe2x80x9csubstratexe2x80x9d and xe2x80x9ctarget portionxe2x80x9d, respectively.
In the present document, the terms xe2x80x9cradiationxe2x80x9d and xe2x80x9cbeamxe2x80x9d are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range 5-20 nm), as well as particle beams, such as ion beams or electron beams.